1. Field of the Invention
The present invention relates to a queue control method and a relay apparatus using the method. More particularly, the present invention relates to a queue control method for a relay apparatus including a plurality of transmit/receive ports which are connected to a LAN (Local Area Network) or a WAN (Wide Area Network) and a relay apparatus using the method.
2. Description of the Related Art
Priority control is performed for relayed flows in some relay apparatuses having transmit/receive ports connected to a LAN or a WAN. Thus, large-scale relay apparatuses having a large number of transmit/receive ports, and relay apparatuses which perform accurate priority control are required. In this specification, “port” is a transmit/receive end, or a transmit/receive end which is connected to a logical circuit established on a physical circuit. “flow” indicates a stream of a specific communication such as a communication between terminals/networks, and a communication between terminals in a specific application.
When implementing priority control by using conventional queue control in the relay apparatus, as shown in FIG. 1, when the relay apparatus is small, a queue control part 12 is provided for a plurality of ports 10a–10x in which the queue control part 12 performs priority control for every flow entered into the relay apparatus from the ports 10a–10x. Flows output from the queue control part 12 are switched by the switch 14 to each destination so as to be output from each corresponding port 10a–10x. 
When the relay apparatus is large or when the relay apparatus accommodates very high-speed circuits, only one queue control part can not support the speed or the size. Thus, as shown in FIG. 2, a configuration can be adopted in which one queue control part is provided to each port in the relay apparatus (or provided to some ports).
However, when there are a plurality of queue control parts 12a–12x exist in a relay apparatus, the priority control is performed only within each of the queue control parts 12a–12x. However, priority control is not performed in the relay apparatus as a whole. For example, when a low priority flow to a specific destination is queued in the queue control part 12a for example and a high priority flow to the same specific destination is queued in the queue control part 12b in which any other flow does not exist, data of the low priority flow is sequentially dequeued from the queue control part 12a so that the data is sent to the switch 14 and data of the high priority flow is sequentially dequeued from the queue control part 12b so that the data is sent to the switch 14.
Thus, the switch 14 performs switching for the two flows at the same ratio. As a result, the low priority flow and the high priority flow are processed in the same priority. Thus, there is problem in that priority control in the relay apparatus as a whole is not realized.
In addition, in a bandwidth control, when a plurality flows in which each dequeue bandwidth is established are concentrated to one destination so that the speed of the flows becomes equal to or greater than a physical circuit speed, dequeue bandwidths are decreased at the same rate for each flow irrespective of the priority of each flow. As a result, there is a problem in that the priorities of the relay apparatus are ignored.